"If you wash a load of just underwear, there will be about 100 million E. coli in the wash water, and they can be transmitted to the next load of laundry," Gerba said.

"There's about a tenth of a gram of poop in the average pair of underwear," he added.

Fecal matter can carry a number of different germs, including the hepatitis A virus, norovirus, rotavirus, salmonella and E. coli.

Philip Tierno, a professor of microbiology and pathology at the New York University School of Medicine and author of the book, "The Secret Life of Germs," said bacteria from the skin, such as staphylococcus, can be found on clothing and towels.

Detergents Are Not The Answer

You may have been relying on your detergent to get rid of all the dirt and germs, but if you're not using bleach or very hot water, you're not killing the bacteria -- they're getting on your hands and staying in the washing machine.

"Most of the hot water people use is not hot enough. You need water that's between 140 and 150 degrees to kill germs," said Tierno.